Electric arc welding system

ABSTRACT

An electric arc welding system and method for creating a first AC welding arc with a first current waveform between a first electrode and a workpiece by a first power supply and a second AC welding arc with a second current waveform between a second electrode and a workpiece by a second power supply as the first and second electrodes are moved in unison along a welding path where the first and second power supply each comprising an high speed switching inverter creating its waveform by a number of current pulses occurring at a frequency of at least 18 kHz with the magnitude of each current pulse controlled by a wave shaper and the polarity of the waveforms controlled by a signal. The first and second AC waveforms each have a positive portion and a negative portion and a cycle period of about 10-20 ms and timing circuits for determining the push and pull times between the arcs and a waveform adjusting circuit to limit the push and pull times to less than about 5.0 ms.

The present invention relates to the art of electric arc welding andmore particularly to an electric arc welding system to operate tandemelectrodes.

INCORPORATION BY REFERENCE

The present invention is directed to an electric arc welding systemutilizing high capacity alternating circuit power supplies for drivingtwo or more tandem electrodes of the type used in seam welding of largemetal blanks. Although the invention can be used with any standard ACpower supply with switches for changing the output polarity, it ispreferred that the power supplies use the switching concept disclosed inStava U.S. Pat. No. 6,111,216 wherein the power supply is an inverterhaving two large output polarity switches with the arc current beingreduced before the switches reverse the polarity. Consequently, the term“switching point” is a complex procedure whereby the power supply isfirst turned off awaiting a current less than a preselected value, suchas 100 amperes. Upon reaching the 100 ampere threshold, the outputswitches of the power supply are reversed to reverse the polarity fromthe D.C. output link of the inverter. Thus, the “switching point” is anoff output command, known as a “kill” command, to the power supplyinverter followed by a switching command to reverse the output polarity.The kill output can be a drop to a decreased current level. Thisprocedure is duplicated at each successive polarity reversal so the ACpower supply reverses polarity only at a low current. In this manner,snubbing circuits for the output polarity controlling switches arereduced in size or eliminated. Since this switching concept is preferredto define the switching points as used in the present invention, StavaU.S. Pat. No. 6,111,216 is incorporated by reference. The concept of anAC current for tandem electrodes is well known in the art. U.S. Pat. No.6,207,929 discloses a system whereby tandem electrodes are each poweredby a separate inverter type power supply. The frequency is varied toreduce the interference between alternating current in the adjacenttandem electrodes. Indeed, this prior patent of assignee relates tosingle power sources for driving either a DC powered electrode followedby an AC electrode or two or more AC driven electrodes. In eachinstance, a separate inverter type power supply is used for eachelectrode and, in the alternating current high capacity power supplies,the switching point concept of Stava U.S. Pat. No. 6,111,216 isemployed. This system for separately driving each of the tandemelectrodes by a separate high capacity power supply is backgroundinformation to the present invention and is incorporated herein as suchbackground. In a like manner, U.S. Pat. No. 6,291,798 discloses afurther arc welding system wherein each electrode in a tandem weldingoperation is driven by two or more independent power supplies connectedin parallel with a single electrode arc. The system involves a singleset of switches having two or more accurately balanced power suppliesforming the input to the polarity reversing switch network operated inaccordance with Stava U.S. Pat. No. 6,111,216. Each of the powersupplies is driven by a single command signal and, therefore, shares theidentical current value combined and directed through the polarityreversing switches. This type system requires large polarity reversingswitches since all of the current to the electrode is passed through asingle set of switches. U.S. Pat. No. 6,291,798 does show a master andslave combination of power supplies for a single electrode and disclosesgeneral background information to which the invention is directed. Forthat reason, this patent is also incorporated by reference. Animprovement for operating tandem electrodes with controlled switchingpoints is disclosed in Houston U.S. Pat. No. 6,472,634. This patent isincorporated by reference.

BACKGROUND OF INVENTION

Welding applications, such as pipe welding, often require high currentsand use several arcs created by tandem electrodes. Such welding systemsare quite prone to certain inconsistencies caused by arc disturbancesdue to magnetic interaction between two adjacent tandem electrodes. Asystem for correcting the disadvantages caused by adjacent AC driventandem electrodes is disclosed in Stava U.S. Pat. No. 6,207,929. In thatprior patent, each of the AC driven electrodes has its own inverterbased power supply. The output frequency of each power supply is variedso as to prevent interference between adjacent electrodes. This systemrequires a separate power supply for each electrode. As the currentdemand for a given electrode exceeds the current rating of the inverterbased power supply, a new power supply must be designed, engineered andmanufactured. Thus, such system for operating tandem welding electrodesrequire high capacity or high rated power supplies to obtain highcurrent as required for pipe welding. To decrease the need for specialhigh current rated power supplies for tandem operated electrodes,assignee developed the system disclosed in Stava U.S. Pat. No. 6,291,798wherein each AC electrode is driven by two or more inverter powersupplies connected in parallel. These parallel power supplies have theiroutput current combined at the input side of a polarity switchingnetwork. Thus, as higher currents are required for a given electrode,two or more parallel power supplies are used. In this system, each ofthe power supplies are operated in unison and share equally the outputcurrent. Thus, the current required by changes in the welding conditionscan be provided only by the over current rating of a single unit. Acurrent balanced system did allow for the combination of several smallerpower supplies; however, the power supplies had to be connected inparallel on the input side of the polarity reversing switching network.As such, large switches were required for each electrode. Consequently,such system overcame the disadvantage of requiring special powersupplies for each electrode in a tandem welding operation of the typeused in pipe welding; but, there is still the disadvantage that theswitches must be quite large and the input, paralleled power suppliesmust be accurately matched by being driven from a single current commandsignal. Stava U.S. Pat. No. 6,291,798 does utilize the concept of asynchronizing signal for each welding cell directing current to eachtandem electrode. However, the system still required large switches.This type of system was available for operation in an ethernet networkinterconnecting the welding cells. In ethernet interconnections, thetiming cannot be accurately controlled. In the system described, theswitch timing for a given electrode need only be shifted on a timebasis, but need not be accurately identified for a specific time. Thus,the described system requiring balancing the current and a single switchnetwork has been the manner of obtaining high capacity current for usein tandem arc welding operations when using an ethernet network or aninternet and ethernet control system. There is a desire to controlwelders by an ethernet network, with or without an internet link. Due totiming limitation, these networks dictated use of tandem electrodesystems of the type using only general synchronizing techniques.

Such systems could be controlled by a network; however, the parameter toeach paralleled power supply could not be varied. Each of the cellscould only be offset from each other by a synchronizing signal. Suchsystems were not suitable for central control by the internet and/orlocal area network control because an elaborate network to merelyprovide offset between cells was not advantageous. Houston U.S. Pat. No.6,472,634 discloses the concept of a single AC arc welding cell for eachelectrode wherein the cell itself includes one or more paralleled powersupplies each of which has its own switching network. The output of theswitching network is then combined to drive the electrode. This allowsthe use of relatively small switches for polarity reversing of theindividual power supplies paralleled in the system. In addition,relatively small power supplies can be paralleled to build a highcurrent input to each of several electrodes used in a tandem weldingoperation. The use of several independently controlled power suppliesparalleled after the polarity switch network for driving a singleelectrode allows advantageous use of a network, such as the internet orethernet.

In Houston U.S. Pat. No. 6,472,634, smaller power supplies in eachsystem are connected in parallel to power a single electrode. Bycoordinating switching points of each paralleled power supply with ahigh accuracy interface, the AC output current is the sum of currentsfrom the paralleled power supplies without combination before thepolarity switches. By using this concept, the ethernet network, with orwithout an internet link, can control the weld parameters of eachparalleled power supply of the welding system. The timing of the switchpoints is accurately controlled by the novel interface, whereas the weldparameters directed to the controller for each power supply can beprovided by an ethernet network which has no accurate time basis. Thus,an internet link can be used to direct parameters to the individualpower supply controllers of the welding system for driving a singleelectrode. There is no need for a time based accuracy of these weldparameters coded for each power supply. In the preferred implementation,the switch point is a “kill” command awaiting detection of a currentdrop below a minimum threshold, such as 100 amperes. When each powersupply has a switch command, then they switch. The switch points betweenparallel power supplies, whether instantaneous or a sequence involving a“kill” command with a wait delay, are coordinated accurately by aninterface card having an accuracy of less than 10 μs and preferably inthe range of 1-5 μs. This timing accuracy coordinates and matches theswitching operation in the paralleled power supplies to coordinate theAC output current.

By using the internet or ethernet local area network, the set of weldparameters for each power supply is available on a less accurateinformation network, to which the controllers for the paralleled powersupplies are interconnected with a high accuracy digital interface card.Thus, the switching of the individual, paralleled power supplies of thesystem is coordinated. This is an advantage allowing use of the internetand local area network control of a welding system. The informationnetwork includes synchronizing signals for initiating several arcwelding systems connected to several electrodes in a tandem weldingoperation in a selected phase relationship. Each of the welding systemsof an electrode has individual switch points accurately controlled whilethe systems are shifted or delayed to prevent magnetic interferencebetween different electrodes. This allows driving of several ACelectrodes using a common information network. The Houston U.S. Pat. No.6,472,634 system is especially useful for paralleled power supplies topower a given electrode with AC current. The switch points arecoordinated by an accurate interface and the weld parameter for eachparalleled power supply is provided by the general information network.This background is technology developed and patented by assignee anddoes not necessarily constitute prior art just because it is herein usedas “background.”

As a feature of the system in Stava U.S. Pat. No. 6,207,929, two or morepower supplies can drive a single electrode. Thus, the system comprisesa first controller for a first power supply to cause the first powersupply to create an AC current between the electrode and workpiece bygenerating a switch signal with polarity reversing switching points ingeneral timed relationship with respect to a given system synchronizingsignal received by the first controller. This first controller isoperated at first welding parameters in response to a set of first powersupply specific parameter signals directed to the first controller.There is provided at least one slave controller for operating the slavepower supply to create an AC current between the same electrode andworkpiece by reversing polarity of the AC current at switching points.The slave controller operates at second weld parameters in response tothe second set of power supply specific parameter signals to the slavecontroller. An information network connected to the first controller andthe second or slave controller contains digital first and second powersupply specific parameter signals for the two controllers and the systemspecific synchronizing signal. Thus, the controllers receive theparameter signals and the synchronizing signal from the informationnetwork, which may be an ethernet network with or without an internetlink, or merely a local area network. The invention involves a digitalinterface connecting the first controller and the slave controller tocontrol the switching points of the second or slave power supply by theswitch signal from the first or master controller. In practice, thefirst controller starts a current reversal at a switch point. This eventis transmitted at high accuracy to the slave controller to start itscurrent reversal process. When each controller senses an arc currentless than a given number, a “ready signal” is created. After a “ready”signal from all paralleled power supplies, all power supplies reversepolarity. This occurs upon receipt of a strobe or look command each 25μs. Thus, the switching is in unison and has a delay of less than 25 μs.Consequently, both of the controllers have interconnected datacontrolling the switching points of the AC current to the singleelectrode. The same controllers receive parameter information and asynchronizing signal from an information network which in practicecomprises a combination of internet and ethernet or a local areaethernet network. The timing accuracy of the digital interface is lessthan about 10 μs and, preferably, in the general range of 1-5 μs. Thus,the switching points for the two controllers driving a single electrodeare commanded within less than 5 μs. Then, switching actually occurswithin 25 μs. At the same time, relatively less time sensitiveinformation is received from the information network also connected tothe two controllers driving the AC current to a single electrode in atandem welding operation. The 25 μs maximum delay can be changed, but isless than the switch command accuracy.

The unique control system disclosed in Houston U.S. Pat. No. 6,472,634is used to control the power supply for tandem electrodes used primarilyin pipe seam welding and disclosed in Stava U.S. Pat. No. 6,291,798.This Stava patent relates to a series of tandem electrodes movable alonga welding path to lay successive welding beads in the space between theedges of a rolled pipe or the ends of two adjacent pipe sections. Theindividual AC waveforms used in this unique technology are created by anumber of current pulses occurring at a frequency of at least 18 kHzwith a magnitude of each current pulse controlled by a wave shaper. Thistechnology dates back to Blankenship U.S. Pat. No. 5,278,390. Shaping ofthe waveforms in the AC currents of two adjacent tandem electrodes isknown and is shown in not only the patents mentioned above, but in StavaU.S. Pat. No. 6,207,929. In this latter Stava patent, the frequency ofthe AC current at adjacent tandem electrodes is adjusted to preventmagnetic interference. All of these patented technologies by The LincolnElectric Company of Cleveland, Ohio have been advances in the operationof tandem electrodes each of which is operated by a separate AC waveformcreated by the waveform technology set forth in these patents. Thesepatents are incorporated by reference herein. However, these patents donot disclose the present invention which is directed to the use of suchwaveform technology for use in tandem welding by adjacent electrodeseach using an AC current. This technology, as the normal transformertechnology, has experienced difficulty in controlling the dynamics ofthe weld puddle. Thus, there is a need for an electric arc weldingsystem for adjacent tandem electrodes which is specifically designed tocontrol the dynamics and physics of the molten weld puddle during thewelding operation. These advantages can not be obtained by merelychanging the frequency to reduce the magnetic interference.

THE INVENTION

The present invention relates to an improvement in the waveformtechnology disclosed in Blankenship U.S. Pat. No. 5,278,390 and used fortandem electrode welding systems by several patents, including StavaU.S. Pat. No. 6,207,929; Stava U.S. Pat. No. 6,291,798; and, HoustonU.S. Pat. No. 6,472,634. The improvement over this well developedtechnology is the control of the AC waveforms generated by adjacenttandem electrodes in a manner where the weld puddle is quiescent duringthe welding operation. This objective is accomplished by using a systemthat controls the relationship between the AC current of adjacent tandemelectrodes to limit the time of concurrent polarity relationships, suchas like polarity and opposite polarity, while obtaining a difference inpenetration and deposition. It has been found that due to arc force onthe weld pool during the times of like polarity in the waveforms of twoadjacent tandem electrodes the molten metal weld pool physicallycollapses whereas during opposite polarity of the waveforms for adjacenttandem electrodes the weld pool is repelled. If the adjacent AC pulseshave a long time, exceeding 20 ms, with a concurrent polarityrelationship, the collapsing or repelling action of the molten metal inthe weld pool is disruptive to the welding process. The resulting weldbead that subsequently solidifies is not uniform. In using an AC currentfor adjacent electrodes, the invention assures that there is no longterm concurrence of any one specific polarity relationship.

The present invention preferably employs the AC/DC Power Wave weldermanufactured and distributed by The Lincoln Electric Company ofCleveland, Ohio. This equipment overcomes the need to trade-off betweenpenetration and deposition in a multi-electrode welding operation. Toaccomplish this objective, the Power Wave power source uses acombination of amplitude and duration together to allow high penetrationand high deposition without increasing average current, which wouldincrease heat input, lower weld metal toughness and increase theelectromagnetic field leading to arc blow and weld puddle instability.The standard practice to increase production rate in submerged arcwelding is to increase the current to a level just below a threshold inwhich the arc becomes unstable. Beyond current increases, further gainsin productivity are made by increasing the number of electrodes, to asmany as six separate electrodes. To achieve the required penetrationwithout excessive reinforcement, a single DC arc is employed as the leadelectrode. Due to the magnetic interaction, only one DC arc can beemployed. This limits the penetration for a given reinforcement level.With the novel technology of the present invention, a DC electrode is nolonger required to achieve the required penetration. For example, thefirst and second arcs are AC waveforms that are shifted to achieve highpenetration with low deposition and the electromagnetic interaction iscontrolled by the phase relationship of the waveforms used in the twotandem electrodes. This arrangement simplifies the customer installationby reducing the number of different types of power sources that arerequired for a given welding operation. Thus, there is a reduction inthe maintenance complexities at the work site.

The invention is directed to a welding system and method wherein severalelectrodes are used in a single weld puddle and controlled in a mannerto minimize the electromagnetic interaction to achieve stability of theweld puddle. The invention utilizes a high speed switching inverter,such as a Power Wave sold by The Lincoln Electric Company that can beadjusted with infinite resolution with waveforms that are adjusted inone degree increments. The adjustment to the waveforms and phaserelationship are accomplished by calculating the time the two adjacentarcs are at the same and opposite polarities. The high speed invertertype waveform controlled power source changes the relationship inaccordance with the invention to achieve balance between the time ofsame polarity and the time of opposite polarity of adjacent AC poweredelectrodes. The balanced time is such that the adjacent electrodes arenot at the same or opposite polarity for a sustained time greater thanabout 5.0 ms. This advantage is achieved by determining the timeadjacent AC waveforms are at the same polarity or at differentpolarities. Then the waveforms are adjusted to minimize the sustainedmaintained time during the welding cycle when the adjacent waveforms areat opposite polarity to “push” the arcs directed toward the weld puddleor like polarities to “pull” the arcs directed toward the weld puddle.This minimizing of the push and pull of the arcs is accomplished duringthe welding process by the use of waveform technology. The waveforms areadjusted to assure that a push or pull condition does not last for morethan about 5.0 ms. To accomplish the invention, a novel system andmethod have been developed.

In accordance with the invention, an electric arc welding system isprovided for creating a first AC welding arc with a first currentwaveform between a first electrode and a workpiece by a first powersupply and a second AC welding arc with a second current waveformbetween a second electrode and a workpiece by a second power supply assaid first and second electrodes are moved in unison along a weldingpath. The first and second electrodes may be any of adjacent AC drivenelectrodes in a group of electrodes used for a single welding operation.Primarily, this invention relates to submerged arc welding used in pipewelding. In accordance with the invention, the first and second powersupplies each comprise a high speed switching inverter creating itswaveform by a number of current pulses at a frequency of at least 18 kHzwith the magnitude of each current pulse controlled by a wave shaper orwave generator and a plurality of the waveforms controlled by a signalas disclosed in Houston U.S. Pat. No. 6,472,634. In accordance with theinvention, the first and second AC waveforms each have a positiveportion and a negative portion and a cycle period of about 10-20 ms. Afirst timing circuit is used for determining the arc push time of asustained maintenance of opposite polarities between the waveforms and awaveform adjusting circuit to limit the arc push time to less than about5.0 ms. In this manner, the push time for the arc is less than about 5.0ms. In accordance with another aspect of the invention, there isprovided a second timing circuit for determining the arc pull time of asustained maintenance of same polarity between the waveforms and awaveform adjusting circuit to limit the pull time of the arc to lessthan about 5.0 ms. The preferred embodiment of the invention involves asystem that limits both the push and pull time for the arcs extendingtoward the weld puddle, so the electric arcs extend verticallydownwardly from adjacent electrodes and do not push away from or pulltoward each other.

In accordance with another aspect of the present invention there isprovided an electric arc welding method for creating a first AC weldingarc with a first current waveform between a first electrode andworkpiece by a first power supply and a second AC welding arc with asecond current waveform between a second electrode and a workpiece by asecond power supply as the first and second electrodes are moved inunison along a welding path. This method employs the system definedabove wherein the push time and/or pull time of the arcs betweenadjacent electrodes are limited to less than about 5.0 ms by adjustingthe shape of waveforms used in the power supplies.

By using the present invention, a weld puddle is controlled so that thearc current of adjacent AC electrodes is substantially vertical towardthe puddle and the puddle remains quiescent. This is the primary objectof the present invention.

Another object of the present invention is the provision of an electricarc welding system for creating two AC welding arcs at adjacent tandemelectrodes which welding system limits the time when there is aconcurrence of a specific polarity relationship.

Still a further object of the present invention is the provision of anelectric arc welding system, as defined above, which welding system isused to perform a method wherein the electromagnetic push and/or theelectromagnetic pull of the arcs for adjacent electrodes are bothlimited to less than about 5.0 ms. By using this method, penetration anddeposition can be optimized without agitating the molten metal in theweld puddle traversed by adjacent AC driven electrodes.

Yet another object of the present invention is the provision of anelectric arc method and/or system, as defined above, which method andsystem controls the dynamics of the weld puddle to prevent puddleagitation and obtain a uniform weld bead.

Still a further object of the present invention is the provision of anelectric arc welding system and method, as defined above, which systemand method utilizes waveform technology to obtain the advantages of aweld puddle control that maintains vertical arcs from adjacentelectrodes driven by AC current from an inverter high speed switchingtype power supply.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of the preferred embodiment of the presentinvention;

FIG. 2 is a wiring diagram of two paralleled power supplies, each ofwhich include a switching output which power supplies are used inpracticing the invention;

FIG. 3 is a cross sectional side view of three tandem electrodesoperated in accordance with the present invention for welding the seamof a pipe;

FIG. 4 is a schematic layout in block form of a welding system for threeelectrodes using the disclosure in Houston U.S. Pat. No. 6,472,634 andStava U.S. Pat. No. 6,291,798;

FIG. 5 is a block diagram showing a single electrode driven by thesystem as shown in FIG. 4 with a variable pulse generator disclosed inHouston U.S. Pat. No. 6,472,634;

FIG. 6 is a current graph for one of two illustrated synchronizingpulses and showing a balanced AC waveform for one tandem electrode;

FIG. 7 is a current graph superimposed upon a signal having logic todetermine the polarity of the waveform as used in practicing the presentinvention;

FIG. 8 is a current graph showing a broad aspect of the preferredembodiment of the present invention;

FIGS. 9 and 10 are schematic drawings illustrating the dynamics of theweld puddle during concurrent polarity relationships of tandemelectrodes to explain the advantage of the present invention;

FIG. 11 is a pair of current graphs showing the waveforms on twoadjacent tandem electrodes employing the present invention;

FIG. 12 is a pair of current graphs of the AC waveforms on adjacenttandem electrodes with areas of concurring polarity relationships;

FIG. 13 are current graphs of the waveforms on adjacent tandemelectrodes wherein the AC waveform of one electrode is substantiallydifferent waveform of the other electrode to limit the time ofconcurrent polarity relationships;

FIG. 14 are current graphs of two sinusoidal waveforms for adjacentelectrodes operated by a system in accordance with the present inventionto use different shaped wave forms for the adjacent electrodes;

FIG. 15 are current graphs showing waveforms at four adjacent AC arcs oftandem electrodes shaped and synchronized in accordance with an aspectof the invention;

FIG. 16 is a schematic layout of the software program to cause switchingof the paralleled power supplies as soon as the coordinated switchcommands have been processed and the next coincident signal has beencreated;

FIG. 17 is a current graph showing the AC current of adjacent electrodesused in tandem welding and employing the present invention;

FIG. 18 is a current graph, similar to the graph in FIG. 17, showing adifferent relationship of the AC current waveforms used at adjacenttandem electrodes and employing the present invention; and,

FIG. 19 is a block diagram illustrating the preferred program, system ormethod of the present invention.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating background technology in FIGS. 1-16 and the preferredembodiment of the invention in FIGS. 17-19. This is not for the purposeof limiting the invention. The preferred system for implementing theinvention is shown in detail in FIGS. 1, 2 AND 16. In FIG. 1 there is asingle electric arc welding system S in the form of a single cell tocreate an alternating current as an arc at weld station WS. This systemor cell includes a first master welder A with output leads 10, 12 inseries with electrode E and workpiece W in the form of a pipe seam jointor other welding operation. Hall effect current transducer 14 provides avoltage in line 16 proportional to the current of welder A. Less timecritical data, such as welding parameters, are generated at a remotecentral control 18. In a like manner, a slave following welder Bincludes leads 20, 22 connected in parallel with leads 10, 12 to directan additional AC current to the weld station WS. Hall effect currenttransducer 24 creates a voltage in line 26 representing current levelsin welder B during the welding operation. Even though a single slave orfollower welder B is shown, any number of additional welders can beconnected in parallel with master welder A to produce an alternatingcurrent across electrode E and workpiece W. The AC current is combinedat the weld station instead of prior to a polarity switching network.Each welder includes a controller and inverter based power supplyillustrated as a combined master controller and power supply 30 and aslave controller and power supply 32. Controllers 30, 32 receiveparameter data and synchronization data from a relatively low levellogic network. The parameter information or data is power supplyspecific whereby each of the power supplies is provided with the desiredparameters such as current, voltage and/or wire feed speed. A low leveldigital network can provide the parameter information; however, the ACcurrent for polarity reversal occurs at the same time. The “same” timeindicates a time difference of less than 10 μs and preferably in thegeneral range of 1-5 μs. To accomplish precise coordination of the ACoutput from power supply 30 and power supply 32, the switching pointsand polarity information can not be provided from a general logicnetwork wherein the timing is less precise. The individual AC powersupplies are coordinated by high speed, highly accurate DC logicinterface referred to as “gateways.” As shown in FIG. 1, power supplies30, 32 are provided with the necessary operating parameters indicated bythe bi-directional leads 42 m, 42 s, respectively. This non-timesensitive information is provided by a digital network shown in FIG. 1.Master power supply 30 receives a synchronizing signal as indicated byunidirectional line 40 to time the controllers operation of its ACoutput current. The polarity of the AC current for power supply 30 isoutputted as indicated by line 46. The actual switching command for theAC current of master power supply 30 is outputted on line 44. The switchcommand tells power supply S, in the form of an inverter, to “kill,”which is a drastic reduction of current. In an alternative, this isactually a switch signal to reverse polarity. The “switching points” orcommand on line 44 preferably is a “kill” and current reversal commandsutilizing the “switching points” as set forth in Stava U.S. Pat. No.6,111,216. Thus, timed switching points or commands are outputted frompower supply 30 by line 44. These switching points or commands mayinvolve a power supply “kill” followed by a switch ready signal at a lowcurrent or merely a current reversal point. The switch “ready” is usedwhen the “kill” concept is implemented because neither inverters are toactually reverse until they are below the set current. This is describedin FIG. 16. The polarity of the switches of controller 30 controls thelogic on line 46. Slave power supply 32 receives the switching point orcommand logic on line 44 b and the polarity logic on line 46 b. Thesetwo logic signals are interconnected between the master power supply andthe slave power supply through the highly accurate logic interface shownas gateway 50, the transmitting gateway, and gateway 52, the receivinggateway. These gateways are network interface cards for each of thepower supplies so that the logic on lines 44 b, 46 b are timed closelyto the logic on lines 44, 46, respectively. In practice, networkinterface cards or gateways 50, 52 control this logic to within 10 μsand preferably within 1-5 μs. A low accuracy network controls theindividual power supplies for data from central control 18 through lines42 m, 42 s, illustrated as provided by the gateways or interface cards.These lines contain data from remote areas (such as central control 18)which are not time sensitive and do not use the accuracy characteristicsof the gateways. The highly accurate data for timing the switch reversaluses interconnecting logic signals through network interface cards 50,52. The system in FIG. 1 is a single cell for a single AC arc; however,the invention is directed to tandem electrodes wherein two or more ACarcs are created to fill the large gap found in pipe welding. Thus, themaster power supply 30 for the first electrode receives asynchronization signal which determines the timing or phase operation ofthe system S for a first electrode, i.e. ARC 1. System S is used withother identical systems to generate ARCs 2, 3, and 4 timed bysynchronizing outputs 84, 86 and 88. This concept is schematicallyillustrated in FIG. 5. The synchronizing or phase setting signals 82-88are shown in FIG. 1 with only one of the tandem electrodes. Aninformation network N comprising a central control computer and/or webserver 60 provides digital information or data relating to specificpower supplies in several systems or cells controlling differentelectrodes in a tandem operation. Internet information 62 is directed toa local area network in the form of an ethernet network 70 having localinterconnecting lines 70 a, 70 b, 70 c. Similar interconnecting linesare directed to each power supply used in the four cells creating ARCs1, 2, 3 and 4 of a tandem welding operation. The description of systemor cell S applies to each of the arcs at the other electrodes. If ACcurrent is employed, a master power supply is used. In some instances,merely a master power supply is used with a cell specific synchronizingsignal. If higher currents are required, the systems or cells include amaster and slave power supply combination as described with respect tosystem S of FIG. 1. In some instances, a DC arc is used with two or moreAC arcs synchronized by generator 80. Often the DC arc is the leadingelectrode in a tandem electrode welding operation, followed by two ormore synchronized AC arcs. A DC power supply need not be synchronized,nor is there a need for accurate interconnection of the polarity logicand switching points or commands. Some DC powered electrodes may beswitched between positive and negative, but not at the frequency of anAC driven electrode. Irrespective of the make-up of the arcs, ethernetor local area network 70 includes the parameter information identifiedin a coded fashion designated for specific power supplies of the varioussystems used in the tandem welding operation. This network also employssynchronizing signals for the several cells or systems whereby thesystems can be offset in a time relationship. These synchronizingsignals are decoded and received by a master power supply as indicatedby line 40 in FIG. 1. In this manner, the AC arcs are offset on a timebasis. These synchronizing signals are not required to be as accurate asthe switching points through network interface cards or gateways 50, 52.Synchronizing signals on the data network are received by a networkinterface in the form of a variable pulse generator 80. The generatorcreates offset synchronizing signals in lines 84, 86 and 88. Thesesynchronizing signals dictate the phase of the individual alternatingcurrent cells for separate electrodes in the tandem operation.Synchronizing signals can be generated by interface 80 or actuallyreceived by the generator through the network 70. In practice, network70 merely activates generator 80 to create the delay pattern for themany synchronizing signals. Also, generator 80 can vary the frequency ofthe individual cells by frequency of the synchronizing pulses if thatfeature is desired in the tandem welding operation.

A variety of controllers and power supplies could be used for practicingthe system as described in FIG. 1; however, preferred implementation ofthe system is set forth in FIG. 2 wherein power supply PSA is combinedwith controller and power supply 30 and power supply PSB is combinedwith controller and power supply 32. These two units are essentially thesame in structure and are labeled with the same numbers whenappropriate. Description of power supply PSA applies equally to powersupply PSB. Inverter 100 has an input rectifier 102 for receiving threephase line current L1, L2, and L3. Output transformer 110 is connectedthrough an output rectifier 112 to tapped inductor 120 for drivingopposite polarity switches Q1, Q2. Controller 140 a of power supply PSAand controller 140 b of PSB are essentially the same, except controller140 a outputs timing information to controller 140 b. Switching pointsor lines 142, 144 control the conductive condition of polarity switchesQ1, Q2 for reversing polarity at the time indicated by the logic onlines 142, 144, as explained in more detail in Stava U.S. Pat. No.6,111,216 incorporated by reference herein. The control is digital witha logic processor; thus, A/D converter 150 converts the currentinformation on feedback line 16 or line 26 to controlling digital valuesfor the level of output from error amplifier 152 which is illustrated asan analog error amplifier. In practice, this is a digital system andthere is no further analog signal in the control architecture. Asillustrated, however, amplifier has a first input 152 a from converter150 and a second input 152 b from controller 140 a or 140 b. The currentcommand signal on line 152 b includes the wave shape or waveformrequired for the AC current across the arc at weld station WS. This isstandard practice as taught by several patents of Lincoln Electric, suchas Blankenship U.S. Pat. No. 5,278,390, incorporated by reference. Seealso Stava U.S. Pat. No. 6,207,929, incorporated by reference. Theoutput from amplifier 152 is converted to an analog voltage signal byconverter 160 to drive pulse width modulator 162 at a frequencycontrolled by oscillator 164, which is a timer program in the processorsoftware. The shape of the waveform at the arcs is the voltage ordigital number at lines 152 b. The frequency of oscillator 164 isgreater than 18 kHz. The total architecture of this system is digitizedin the preferred embodiment of the present invention and does notinclude reconversion back into analog signal. This representation isschematic for illustrative purposes and is not intended to be limitingof the type of power supply used in practicing the present invention.Other power supplies could be employed.

The practice of the present invention utilizing the concepts of FIGS. 1and 2 are illustrated in FIGS. 3 and 4. Workpiece 200 is a seam in apipe which is welded together by tandem electrodes 202, 204 and 206powered by individual power supplies PS1, PS2, PS3, respectively. Thepower supplies can include more than one power source coordinated inaccordance with the technology in Houston U.S. Pat. No. 6,472,634. Theillustrated embodiment involves a DC arc for lead electrode 202 and anAC arc for each of the tandem electrodes 204, 206. The created waveformsof the tandem electrodes are AC currents and include shapes created by awave shaper or wave generator in accordance with the previouslydescribed waveform technology. As electrodes 202, 204 and 206 are movedalong weld path WP a molten metal puddle P is deposited in pipe seam 200with an open root portion 210 followed by deposits 212, 214 and 216 fromelectrodes 202, 204 and 206, respectively. As previously described morethan two AC driven electrodes as will be described and illustrated bythe waveforms of FIG. 15, can be operated by the invention relating toAC currents of adjacent electrodes. The power supplies, as shown in FIG.4, each include an inverter 220 receiving a DC link from rectifier 222.In accordance with Lincoln waveform technology, a chip or internalprogrammed pulse width modulator stage 224 is driven by an oscillator226 at a frequency greater than 18 kHz and preferably greater than 20kHz. As oscillator 226 drives pulse width modulator 224, the outputcurrent has a shape dictated by the wave shape outputted from waveshaper 240 as a voltage or digital numbers at line 242. Output leads217, 218 are in series with electrodes 202, 204 and 206. The shape inreal time is compared with the actual arc current in line 232 from HallEffect transducer 228 by a stage illustrated as comparator 230 so thatthe outputs on line 234 controls the shape of the AC waveforms. Thedigital number or voltage on line 234 determines the output signal online 224 a to control inverter 220 so that the waveform of the currentat the arc follows the selected profile outputted from wave shaper 240.This is standard Lincoln waveform technology, as previously discussed.Power supply PS1 creates a DC arc at lead electrode 202; therefore, theoutput from wave shaper 240 of this power supply is a steady stateindicating the magnitude of the DC current. The present invention doesnot relate to the formation of a DC arc. To the contrary, the presentinvention is the control of the current at two adjacent AC arcs fortandem electrodes, such as electrodes 204, 206. In accordance with theinvention, wave shaper 240 involves an input 250 employed to select thedesired shape or profile of the AC waveform. This shape can be shiftedin real time by an internal programming schematically represented asshift program 252. Wave shaper 240 has an output which is a prioritysignal on line 254. In practice, the priority signal is a bit of logic,as shown in FIG. 7. Logic 1 indicates a negative polarity for thewaveform generated by wave shaper 240 and logic 0 indicates a positivepolarity. This logic signal or bit controller 220 directed to the powersupply is read in accordance with the technology discussed in FIG. 16.The inverter switches from a positive polarity to a negative polarity,or the reverse, at a specific “READY” time initiated by a change of thelogic bit on line 254. In practice, this bit is received from variablepulse generator 80 shown in FIG. 1 and in FIG. 5. The welding systemshown in FIGS. 3 and 4 is used in practicing the invention wherein theshape of AC arc currents at electrodes 204 and 206 have novel shapes toobtain a beneficial result of the present invention, i.e. a generallyquiescent molten metal puddle P and/or synthesized sinusoidal waveformscompatible with transformer waveforms used in arc welding. The electricarc welding system shown in FIGS. 3 and 4 have a program to select thewaveform at “SELECT” program 250 for wave shaper 240. In this manner theunique waveforms of the present invention are used by the tandemelectrodes. One of the power supplies to create an AC arc isschematically illustrated in FIG. 5. The power supply or source iscontrolled by variable pulse generator 80, shown in FIG. 1. Signal 260from the generator controls the power supply for the first arc. Thissignal includes the synchronization of the waveform together with thepolarity bit outputted by the wave shaper 240 on line 254. Lines 260a-260 n control the desired subsequent tandem AC arcs operated by thewelding system of the present invention. The timing of these signalsshifts the start of the other waveforms. FIG. 5 merely shows therelationship of variable pulse generator 80 to control the successivearcs as explained in connection with FIG. 4.

In the welding system of Houston U.S. Pat. No. 6,472,634, the ACwaveforms are created as shown in FIG. 6 wherein the wave shaper for arcAC1 at electrode 204 creates a signal 270 having positive portions 272and negative portions 274. The second arc AC2 at electrode 206 iscontrolled by signal 280 from the wave shaper having positive portions282 and negative portions 284. These two signals are the same, but areshifted by the signal from generator 80 a distance x, as shown in FIG.6. The waveform technology created current pulses or waveforms at one ofthe arcs are waveforms having positive portions 290 and negativeportions 292 shown at the bottom portion of FIG. 6. A logic bit from thewave shaper determines when the waveform is switched from the positivepolarity to the negative polarity and the reverse. In accordance withthe disclosure in Stava U.S. Pat. No. 6,111,216 (incorporated byreference herein) pulse width modulator 224 is generally shifted to alower level at point 291 a and 291 b. Then the current reduces untilreaching a fixed level, such as 100 amps. Consequently, the switcheschange polarity at points 294 a and 294 b. This produces a vertical lineor shape 296 a, 296 b when current transitioning between positiveportion 290 and negative portion 292. This is the system disclosed inthe Houston patent where the like waveforms are shifted to avoidmagnetic interference. The waveform portions 290, 292 are the same atarc AC1 and at arc AC2. This is different from the present inventionwhich relates to customizing the waveforms at arc AC1 and arc AC2 forpurposes of controlling the molten metal puddle and/or synthesizing asinusoidal wave shape in a manner not heretofore employed. Thedisclosure of FIG. 6 is set forth to show the concept of shifting thewaveforms, but not the invention which is customizing each of theadjacent waveforms. The same switching procedure to create a verticaltransition between polarities is used in the preferred embodiment of thepresent invention. Converting from the welding system shown in FIG. 6 tothe present invention is generally shown in FIG. 7. The logic on line254 is illustrated as being a logic 1 in portions 300 and a logic 0 inportions 302. The change of the logic or bit numbers signals the timewhen the system illustrated in FIG. 16 shifts polarity. This isschematically illustrated in the lower graph of FIG. 6 at points 294 a,294 b. In accordance with the invention, wave shaper 240 for each of theadjacent AC arcs has a first wave shape 310 for one of the polaritiesand a second wave shape 312 for the other polarity. Each of thewaveforms 310, 312 are created by the logic on line 234 taken togetherwith the logic on line 254. Thus, pulses 310, 312 as shown in FIG. 7,are different pulses for the positive and negative polarity portions.Each of the pulses 310, 312 are created by separate and distinct currentpulses 310 a, 312 a as shown. Switching between polarities isaccomplished as illustrated in FIG. 6 where the waveforms generated bythe wave shaper are shown as having the general shape of waveforms 310,312. Positive polarity controls penetration and negative polaritycontrols deposition. In accordance with the invention, the positive andnegative pulses of a waveform are different and the switching points arecontrolled so that the AC waveform at one arc is controlled both in thenegative polarity and the positive polarity to have a specific shapecreated by the output of wave shaper 240. The waveforms for the arcadjacent to the arc having the current shown in FIG. 7 is controlleddifferently to obtain the advantages of the present invention. This isillustrated best in FIG. 8. The waveform at arc AC1 is in the top partof FIG. 8. It has positive portions 320 shown by current pulses 320 aand negative portions 322 formed by pulses 322 a. Positive portion 320has a maximum magnitude a and width or time period b. Negative portion322 has a maximum magnitude d and a time or period c. These fourparameters are adjusted by wave shaper 240. In the illustratedembodiment, arc AC2 has the waveform shown at the bottom of FIG. 8 wherepositive portion 330 is formed by current pulses 330 a and has a heightor magnitude a′ and a time length or period b′. Negative portion 332 isformed by pulses 332 a and has a maximum magnitude d′ and a time lengthc′. These parameters are adjusted by wave shaper 240. In accordance withthe invention, the waveform from the wave shaper on arc AC1 is out ofphase with the wave shape for arc AC2. The two waveforms have parametersor dimensions which are adjusted so that (a) penetration and depositionis controlled and (b) there is no long time during which the puddle P issubjected to a specific polarity relationship, be it a like polarity oropposite polarity. This concept in formulating the wave shapes preventslong term polarity relationships as explained by the showings in FIGS. 9and 10. In FIG. 9 electrodes 204, 206 have like polarity, determined bythe waveforms of the adjacent currents at any given time. At thatinstance, magnetic flux 350 of electrode 204 and magnetic flux 352 ofelectrode 206 are in the same direction and cancel each other at centerarea 354 between the electrodes. This causes the molten metal portions360, 362 from electrodes 204, 206 in the molten puddle P to movetogether, as represented by arrows c. The arcs are pulled together sothe arc force on the weld puddle moves the metal together. This inwardmovement together or collapse of the molten metal in puddle P betweenelectrodes 204 will ultimately cause an upward gushing action, if notterminated in a very short time, i.e. less than about 20 ms. As shown inFIG. 10, the opposite movement of the puddle occurs when the electrodes204, 206 have opposite polarities. Then, magnetic flux 370 and magneticflux 372 are accumulated and increased in center portion 374 between theelectrodes. High forces between the electrodes causes the molten metalportions 364, 366 of puddle P to retract or be forced away from eachother. This is indicated by arrows r. The arcs are pushed apart so thearc force on the weld puddle moves the metal apart. Such outward forcingof the molten metal in puddle P causes disruption of the weld bead if itcontinues for a substantial time which is generally less than 10 ms. Ascan be seen from FIGS. 9 and 10, it is desirable to limit the timeduring which the polarity of the waveform at adjacent electrodes iseither the same polarity or opposite polarity. The present inventionutilizes the waveform, such as shown in FIG. 6, to accomplish thisobjective of preventing long term concurrence of specific polarityrelationships, be it like polarities or opposite polarities. Both ofthese relationships are detrimental to quality welding and are avoidedwhen using the present invention. As shown in FIG. 8, like polarity andopposite polarity is retained for a very short time less than the cyclelength of the waveforms at arc AC1 and arc AC2. This positivedevelopment of preventing long term occurrence of polarity relationshipstogether with the novel concept of pulses having different shapes anddifferent proportions in the positive and negative areas combine tocontrol the puddle, control penetration and control deposition in amanner not heretofore obtainable in welding with a normal transformerpower supplies or normal use of Lincoln waveform technology.

An implementation of the present invention is shown in FIG. 11 whereinthe positive and negative portions of the AC waveform from the waveshaper 240 are synthesized sinusoidal shapes with a different energy inthe positive portion as compared to the negative portion of thewaveforms. The synthesized sine wave or sinusoidal portions of thewaveforms is novel. It allows the waveforms to be compatible withtransformer welding circuits and compatible with evaluation of sine wavewelding. In FIG. 11, waveform 370 is at arc AC1 and waveform 372 is atarc AC2. These tandem arcs utilize the AC welding current shown in FIG.11 wherein a small positive sinusoidal portion 370 a controlspenetration at arc AC1 while the larger negative portion 370 b controlsthe deposition of metal at arc AC1. There is a switching between thepolarities with a change in the logic bit, as discussed in FIG. 7.Sinusoidal waveform 370 plunges vertically from approximately 100amperes through zero current as shown in by vertical line 370 c.Transition between the negative portion 370 b and positive portion 370 aalso starts a vertical transition at the switching point causing avertical transition 370 d. In a like manner, phase shifted waveform 372of arc AC2 has a small penetration portion 372 a and a large negativedeposition portion 372 b. Transition between polarities is indicated byvertical lines 372 c and 372 d. Waveform 372 is shifted with respect towaveform 370 so that the dynamics of the puddle are controlled withoutexcessive collapsing or repulsion of the molten metal in the puddlecaused by polarities of adjacent arcs AC1, AC2. In the embodiment shownin FIG. 11, the sine wave shapes are the same and the frequencies arethe same. They are merely shifted to prevent a long term occurrence of aspecific polarity relationship.

Another aspect of the invention is schematically illustrated in FIG. 12wherein waveform 380 is used for arc AC1 and waveform 382 is used forarc AC2. Portions 380 a, 380 b, 382 a, and 382 b are sinusoidalsynthesized and are illustrated as being of the same general magnitude.By shifting these two waveforms 900, areas of concurrent polarity areidentified as areas 390, 392, 394 and 396. By using the shiftedwaveforms with sinusoidal profiles, like polarities or oppositepolarities do not remain for any length of time. Thus, the molten metalpuddle is not agitated and remains quiescent. This advantage is obtainedby using the present invention which also combines the concept of adifference in energy between the positive and negative polarity portionsof a given waveform. FIG. 12 is illustrative in nature to show thedefinition of concurrent polarity relationships and the fact that theyshould remain for only a short period of time. To accomplish thisobjective, another embodiment of the present invention is illustrated inFIG. 13 wherein previously defined waveform 380 is combined withwaveform 400, shown as the sawtooth waveform of arc AC2(a) or thepulsating waveform 402 shown as the waveform for arc AC2(b). Combiningwaveform 380 with the different waveform 400 of a different waveform 402produces very small areas or times of concurrent polarity relationships410, 412, 414, etc. The invention illustrated in FIG. 14 has the ACwaveform generated at one arc drastically different than the AC waveformgenerated at the other arc. This same concept of drastically differentwaveforms for use in the present invention is illustrated in FIG. 14wherein waveform 420 is an AC pulse profile waveform and waveform 430 isa sinusoidal profile waveform having about one-half the period ofwaveform 420. Waveform 420 includes a small penetration positive portion420 a and a large deposition portion 420 b with straight line polaritytransitions 420 c. Waveform 430 includes positive portion 430 a andnegative portion 430 b with vertical polarity transitions 430 c. Byhaving these two different waveforms, both the synthesized sinusoidalconcept is employed for one electrode and there is no long termconcurrent polarity relationship. Thus, the molten metal in puddle Premains somewhat quiescent during the welding operation by both arcsAC1, AC2.

Another aspect of the present invention is illustrated in FIG. 15wherein waveforms 450, 452, 454 and 456 are generated by the wave shaper240 of the power supply for each of four tandem arcs, arc AC1, arc AC2,arc AC3 and arc AC4. The adjacent arcs are aligned as indicated bysynchronization signal 460 defining when the waveforms correspond andtransition from the negative portion to the positive portion. Thissynchronization signal is created by generator 80 shown in FIG. 1,except the start pulses are aligned. In this embodiment of the inventionfirst waveform 450 has a positive portion 450 a, which is synchronizedwith both the positive and negative portion of the adjacent waveform452, 454 and 456. For instance, positive portion 450 a is synchronizedwith and correlated to positive portion 452 a and negative portion 452 bof waveform 452. In a like manner, the positive portion 452 a ofwaveform 452 is synchronized with and correlated to positive portion 454a and negative portion 454 b of waveform 454. The same relationshipexist between positive portion 454 a and the portions 456 a, 456 b ofwaveform 456. The negative portion 450 b is synchronized with andcorrelated to the two opposite polarity portions of aligned waveform452. The same timing relationship exist between negative portion 452 band waveform 454. In other words, in each adjacent arc one polarityportion of the waveform is correlated to a total waveform of theadjacent arc. In this manner, the collapse and repelling forces ofpuddle P, as discussed in connection with FIGS. 9 and 10, aredynametically controlled. In this embodiment of the invention, one ormore of the positive or negative portions can be synthesized sinusoidalwaves as discussed in connection with an aspect of the inventiondisclosed in FIGS. 11 and 12.

As indicated in FIGS. 1 and 2, when the master controller of switches isto switch, a switch command is issued to master controller 140 a ofpower supply 30. This causes a “kill” signal to be received by themaster so a kill signal and polarity logic is rapidly transmitted to thecontroller of one or more slave power supplies connected in parallelwith a single electrode. If standard AC power supplies are used withlarge snubbers in parallel with the polarity switches, the slavecontroller or controllers are immediately switched within 1-10 μs afterthe master power supply receives the switch command. This is theadvantage of the high accuracy interface cards or gateways. In practice,the actual switching for current reversal of the paralleled powersupplies is not to occur until the output current is below a givenvalue, i.e. about 100 amperes. This allows use of smaller switches.

The implementation of the switching for all power supplies for a singleAC arc uses the delayed switching technique where actual switching canoccur only after all power supplies are below the given low currentlevel. The delay process is accomplished in the software of the digitalprocessor and is illustrated by the schematic layout of FIG. 16. Whenthe controller of master power supply 500 receives a command signal asrepresented by line 502, the power supply starts the switching sequence.The master outputs a logic on line 504 to provide the desired polarityfor switching of the slaves to correspond with polarity switching of themaster. In the commanded switch sequence, the inverter of master powersupply 500 is turned off or down so current to electrode E is decreasedas read by hall effect transducer 510. The switch command in line 502causes an immediate “kill” signal as represented by line 512 to thecontrollers of paralleled slave power supplies 520, 522 providingcurrent to junction 530 as measured by hall effect transducers 532, 534.All power supplies are in the switch sequence with inverters turned offor down. Software comparator circuits 550, 552, 554 compare thedecreased current to a given low current referenced by the voltage online 556. As each power supply decreases below the given value, a signalappears in lines 560, 562, and 564 to the input of a sample and holdcircuits 570, 572, and 574, respectively. The circuits are outputted bya strobe signal in line 580 from each of the power supplies. When a setlogic is stored in a circuit 570, 572, and 574, a YES logic appears onlines READY¹, READY², and READY³ at the time of the strobe signal. Thissignal is generated in the power supplies and has a period of 25 μs;however, other high speed strobes could be used. The signals aredirected to controller C of the master power supply, shown in dashedlines in FIG. 8. A software ANDing function represented by AND gate 580has a YES logic output on line 582 when all power supplies are ready toswitch polarity. This output condition is directed to clock enableterminal ECLK of software flip flop 600 having its D terminal providedwith the desired logic of the polarity to be switched as appearing online 504. An oscillator or timer operated at about 1 MHz clocks flipflop by a signal on line 602 to terminal CK. This transfers the polaritycommand logic on line 504 to a Q terminal 604 to provide this logic inline 610 to switch slaves 520, 522 at the same time the identical logicon line 612 switches master power supply 500. After switching, thepolarity logic on line 504 shifts to the opposite polarity while masterpower supply awaits the next switch command based upon the switchingfrequency. Other circuits can be used to effect the delay in theswitching sequence; however, the illustration in FIG. 16 is the presentscheme.

The present application relates to the waveforms controlled by a waveshaper or waveform generator of an electric arc power supply including asingle power source or multiple power sources correlated as disclosed inHouston U.S. Pat. No. 6,472,634 or Stava U.S. Pat. No. 6,291,798. Theinvention relates to tandem electrodes powered by an AC waveform. Thetwo adjacent electrodes have waveforms that control the dynamics of themolten metal puddle between the electrodes and/or uses synthesized sinewaves to correlate the operation of the tandem welding system withstandard transformer welding operations. The invention involvescontrolling the energy of the positive and negative portions in each ofthe AC waveforms created by a wave shaper or waveform generator throughthe use of a high speed switching inverter in accordance with standardpractice. Different energy in the positive portion and negative portioncontrols the relationship of the amount of penetration to the amount ofdeposition by a particular electrode. This allows operation of adjacentelectrodes in a manner to maintain the weld puddle generally quiescent.This action improves the resulting weld bead and the efficiency of thewelding operation. To control the weld puddle, adjacent waveformsgenerated by the wave shaper have different shapes to control the lengthof time during which a given polarity relationship exist between theadjacent electrodes. In other words, the time that the waveforms ofadjacent electrodes have like polarity or opposite polarity is limitedby using different shapes and different relationships between the twoadjacent AC waveforms generated by the waveform technology using a waveshaper or waveform generator. As disclosed in FIG. 15, synchronizing thewave shapes of adjacent generated waveforms having a frequency ofadjacent electrodes which is essentially a multiple of two. All of theseunique waveforms are novel and provide beneficial results in an electricarc welding using tandem electrodes, especially for seam welding ofpipes in making pipeline sections.

In FIG. 4, a system and method is illustrated utilizing a leading DCelectrode following by tandem AC driven electrodes AC1 and AC2. Thepresent invention is primarily applicable to a submerged arc weldingoperation including merely a plurality of tandem electrodes each drivenby a AC waveform constructed by a wave shaper or waveform generator inaccordance with waveform technology used in the Power Wave power sourcesold by The Lincoln Electric Company of Cleveland, Ohio. This powersource is capable of changing the waveform of each electrode inincrements of one degree. The invention relates to controlling the ACcurrent waveforms of adjacent electrodes. The electrodes may be thefirst and second, second and third, third and fourth, fourth and fifth,fifth and sixth, etc. The adjacent electrodes driven by an AC currentwaveform created by a waveform generator or wave shaper. The inventionuses a cored electrode to assist in transition between positive andnegative polarities. The invention will be described in connection withspecific AC pulse waveforms, as shown in FIGS. 17 and 18 illustratingrepresentative waveforms for adjacent tandem electrodes. In FIG. 17,curve or waveform 700 has a positive portion 702 and a negative portion704. For illustrative and explanatory purposes, waveform or currentcurve 700 is divided into segments 710, 712, 714 and 716. Waveform 720for the arc of the second electrode has a positive portion 722 and anegative portion 724. Four waveform segments 730, 732, 734 and 736 arealigned with the corresponding waveform segments 710, 712, 714 and 716,respectively.

During welding, the two arcs are moved along the weld path. The adjacentarcs are in a “push” condition at segments 710, 724. These segments haveopposite polarity so the arcs are pushed away from each other. In thenext aligned segment area, segments 712 and 732 are at the same polarityso the arcs tend to pull together. During the weld cycle indicated bywaveform or curve 700, the arcs are alternately pushed apart and pulledtogether at each change in condition of the polarity relationship. Thewaveforms have a cycle length of between 10-20 ms and, thus, eachsegment is approximately 2.5-5.0 ms in length. In accordance with theinvention, the waveforms 700, 720 of adjacent electrodes are controlledso that the push and pull events are sustained less than about 5.0 ms.If the push condition is maintained for a longer time, the weld puddleis affected and the arcs spread to change the stability of the weldingprocess. In a like manner, if a pull condition is maintained for aprolonged time, the arcs of the adjacent electrodes pull together andaffect the puddle dynamics. The present invention relates to adjacentwaveforms having alternate push and pull conditions dictated by thepolarity relationships wherein the waveforms are adjusted so themaintained or sustained time of either a push condition or a pullcondition is less than about 5.0 ms. This method is illustrated in FIG.17. The same method is illustrated in FIG. 18 wherein the cycle lengthis still 10-20 ms. Waveform or curve 740 of the first arc has positiveportions 742 and negative portions 744. For illustrative and explanatorypurposes, curve or waveform 740 is divided into time segments 750, 752,754, and 756. Due to the shape of waveform 740, a fifth time segment 758is identified. This last segment is a duplicate of leading segment 750.The adjacent electrode has a second arc shown as curve or waveform 760with positive portions 762 and negative portions 764. To correspond withthe segments of waveform 740, waveform 760 is divided into segments 770,772, 774 and 776. The two waveforms are adjusted so that the positivedeposition portion is correlated with the negative penetration portionin accordance with standard welding technology. By providing greaterpenetration with the electrode using waveform 740 and higher depositionwith the electrode using waveform 760 the welding operation iscustomized. When this is done, there is a problem of prolonged periodsof arc push or arc pull. In accordance with the present invention,waveforms as shown in FIG. 17 or FIG. 18 are created to avoid prolongedperiods of push or pull.

In FIG. 18, segments 750, 770 have opposite polarities; therefore, anarc push condition exists. In the area of the waveforms defined bysegments 752 and 772, the polarities are the same; therefore, there isan arc pull condition. Each of the curves are divided by four so the arcpush and arc pull conditions alternate as illustrated in FIG. 18. Thesame alternating procedure is illustrated in the waveforms of twoadjacent electrodes as disclosed in FIG. 17. The waveforms need not havethe same cycle length, nor equal positive and negative magnitudes. Thepositive and negative magnitudes are adjusted to control deposition andpenetration by the arcs. In accordance with the invention, the waveformsof adjacent electrodes, as shown in FIGS. 17 and 18, are adjusted sothat the sustained and/or maintained time of a push or pull condition islimited to less than about 5.0 ms. The waveforms can be sinusoidal orpulsed AC waveforms, as shown in FIGS. 17 and 18. The system and methodof the present invention relates to limiting the amount of time ofeither an arc push or an arc pull condition.

The preferred program or method processed by the controller of the powersupplies. To perform the present invention, program or method 800 shownin FIG. 19 is practiced by the digital section of the controller whichsection is normally a DSP or microprocessor. Preferably method 800 isperformed by the controller of a Power Wave power source. As illustratedin FIG. 19, the cycle length of the waveforms of adjacent electrodes areindicated by blocks 802, 804. In the preferred embodiment, these twoblocks are identical using the same cycle length of about 10-20 ms. Thepolarity of the individual arcs is determined by detectors 810, 812reading the arc polarities of the method at any given time. The polarityof adjacent arcs is communicated from detectors 810, 812 to comparatornetwork 820. If the polarities are opposite, an arc push conditionexist. This creates a logic signal in line 822. If the polarities arethe same, a logic signal appears in line 824. This signal indicates apull condition for the arc. Of course, if either waveform is at zero,there is no push or pull condition. Referring now to a push conditionwith a logic 1 in line 822, which is a YES signal from network 820. Timecounter 830 is started by the logic signal in line 822 to count inaccordance with clock 832. Although not necessary in all instances, areset circuit 834 creates a digital signal in line 836 to reset counter830 at the end of cycle 804. The output of counter 830 is directed to adecision device or network 840. If the counter reaches a level greaterthan about 5.0 ms, a YES signal is created in line 842. This YES signalactivates waveform adjust routine 850 to create an adjusting signal inlines 852, 854 for changing the wave shape created by generators 740 a,740 b. In this manner, pulse width modulators 224 a, 224 b are adjustedto operate Power Wave inverter power sources 220 a, 220 b for thepurpose of adjusting the AC waveforms at ARC 1, ARC 2. In this manner, awaveform adjustment is made to assure that the push condition does nothave a sustained existence greater than about 5.0 ms.

In a like manner, program or method 800 controls the pull condition ofthe arcs between adjacent electrodes. When there is a pull condition,due to a like polarity between the adjacent waveforms, a YES signalappears in line 824 to start the pull time counter 860. The counter isdriven by clock 862. In accordance with a feature not necessary inpracticing the invention, reset 864 creates a digital signal representedby a signal on line 866 to reset counter 860 at the end of each cycle802. A decision device 870 determines whether the pull condition ismaintained or sustained for greater than about 5.0 ms. If the decisiondevice creates a YES signal in line 872, adjust routine 880 is activatedto adjust the signal in lines 882, 884 directed to the two wave shapegenerators or wave shapers 240 a, 240 b to adjust the operation of pulsewidth modulators 224 a, 224 b for adjusting the operation of the powerwave inverter power sources 220 a, 220 b. This adjusts the arc ARC 1 andarc ARC 2 to assure that a push condition does not last for greater thanabout 5.0 ms. Since a push condition and a pull condition are oppositeevents, a coincidence network 890 is employed in program 800. Thisnetwork includes an enable signal in line 892 from counter 830 and anenable signal in line 894 from counter 860. Inverter gates 896, 898 inlines 892, 894, respectively, change the logic on lines 892, 894. Thus,when time 830 is not operating, timer 860 is enabled. In a like manner,when timer 860 is not operating, timer 830 is enabled. Thus, the twocounters 830, 860 are not operated at the same time. By using program ormethod 800, the sustained time of either a push condition or a pullcondition between adjacent AC driven electrodes is limited by adjustingwave shape generator through the controller of a Power Wave welder.These wave shape generators can be adjusted manually to accomplish theobjective of method 800. Manual adjustment can be made visually byobserving the dynamics of the weld puddle. However, method 800 ispreferably performed in the digital controller of the welder. The time5.0 ms is preferred; however, this value is not critical, but it's morea general magnitude. The use of this time designation, teaches a personskilled in the art how to accomplish the objectives of the invention.

1. An electric arc welding system for creating a first AC welding arcwith a first current waveform between a first electrode and a workpieceby a first power supply and a second AC welding arc with a secondcurrent waveform between a second electrode and a workpiece by a secondpower supply as said first and second electrodes are moved in unisonalong a welding path, said first and second power supply each comprisingan high speed switching inverter creating its waveform by a number ofcurrent pulses occurring at a frequency of at least 18 kHz with themagnitude of each current pulse controlled by a wave shaper and thepolarity of said waveforms controlled by a signal, wherein said firstand second AC waveforms have a positive portion and a negative portionand a cycle period of about 10-20 ms, a first timing circuit fordetermining the push time of a sustained maintenance of oppositepolarity between said waveforms and a waveform adjusting circuit tolimit said push time to less than about 5.0 ms.
 2. An electric arcwelding system as defined in claim 1 wherein said AC waveforms aregenerally sinusoidal.
 3. An electric arc welding system as defined inclaim 2 including a second timing circuit for determining the pull timeof a sustained maintenance of the same polarity between said waveformsand a second waveform adjusting circuit to limit said pull time to lessthan about 5.0 ms.
 4. An electric arc welding system as defined in claim1 including a second timing circuit for determining the pull time of asustained maintenance of the same polarity between said waveforms and asecond waveform adjusting circuit to limit said pull time to less thanabout 5.0 ms.
 5. An electric arc welding system as defined in claim 4wherein one of said waveforms is generally a square AC waveform.
 6. Anelectric arc welding system as defined in claim 1 wherein one of saidwaveforms is generally a square AC waveform.
 7. An electric arc weldingsystem as defined in claim 4 wherein both of said waveforms aregenerally a square AC waveform.
 8. An electric arc welding system asdefined in claim 1 wherein both of said waveforms are generally a squareAC waveform.
 9. An electric arc welding system as defined in claim 4wherein one of said waveforms is a pulse AC waveform.
 10. An electricarc welding system as defined in claim 1 wherein one of said waveformsis a pulse AC waveform.
 11. An electric arc welding system for creatinga first AC welding arc with a first current waveform between a firstelectrode and a workpiece by a first power supply and a second ACwelding arc with a second current waveform between a second electrodeand a workpiece by a second power supply as said first and secondelectrodes are moved in unison along a welding path, said first andsecond power supply each comprising an high speed switching invertercreating its waveform by a number of current pulses occurring at afrequency of at least 18 kHz with the magnitude of each current pulsecontrolled by a wave shaper and the polarity of said waveformscontrolled by a signal, wherein said first and second AC waveforms havea positive portion and a negative portion and a cycle period of about10-20 ms, a timing circuit for determining the pull time of a sustainedmaintenance of same polarity between said waveforms and a waveformadjusting circuit to limit said pull time to less than about 5.0 ms. 12.An electric arc welding system as defined in claim 11 wherein said ACwaveforms are generally sinusoidal.
 13. An electric arc welding systemas defined in claim 12 wherein one of said waveforms is generally asquare AC waveform.
 14. An electric arc welding system as defined inclaim 11 wherein one of said waveforms is generally a square ACwaveform.
 15. An electric arc welding system as defined in claim 12wherein both of said waveforms are generally a square AC waveform. 16.An electric arc welding system as defined in claim 11 wherein both ofsaid waveforms are generally a square AC waveform.
 17. An electric arcwelding system as defined in claim 12 wherein one of said waveforms is apulse AC waveform.
 18. An electric arc welding system as defined inclaim 11 wherein one of said waveforms is a pulse AC waveform.
 19. Anelectric arc welding method for creating a first AC welding arc with afirst current waveform between a first electrode and a workpiece by afirst power supply and a second AC welding arc with a second currentwaveform between a second electrode and a workpiece by a second powersupply as said first and second electrodes are moved in unison along awelding path, said first and second power supply each comprising an highspeed switching inverter creating its waveform by a number of currentpulses occurring at a frequency of at least 18 kHz with the magnitude ofeach current pulse controlled by a wave shaper and the polarity of saidwaveforms controlled by a signal, wherein said first and second ACwaveform have a positive portion and a negative portion and a cycleperiod of about 10-20 ms, said method comprising: (a) determining thepush time of a sustained maintenance of opposite polarity between saidwaveforms; and, (b) adjusting said waveforms to limit said push time toless than about 5.0 ms.
 20. An electric arc welding method as defined inclaim 19 wherein said AC waveforms are generally sinusoidal.
 21. Anelectric arc welding method as defined in claim 20 further including:(c) determining the pull time of a sustained maintenance of the samepolarity between said waveforms; and, (d) adjusting said waveforms tolimit said pull time to less than about 5.0 ms.
 22. An electric arcwelding method as defined in claim 19 including a second timing circuitfor determining the pull time of a sustained maintenance of the samepolarity between said waveforms and a second waveform adjusting circuitto limit said pull time to less than about 5.0 ms.
 23. An electric arcwelding method as defined in claim 22 wherein one of said waveforms isgenerally a square AC waveform.
 24. An electric arc welding method asdefined in claim 19 wherein one of said waveforms is generally a squareAC waveform.
 25. An electric arc welding method as defined in claim 22wherein both of said waveforms are generally a square AC waveform. 26.An electric arc welding method as defined in claim 19 wherein both ofsaid waveforms are generally a square AC waveform.
 27. An electric arcwelding method as defined in claim 22 wherein one of said waveforms is apulse AC waveform.
 28. An electric arc welding method as defined inclaim 19 wherein one of said waveforms is a pulse AC waveform.
 29. Anelectric arc welding method for creating a first AC welding arc with afirst current waveform between a first electrode and a workpiece by afirst power supply and a second AC welding arc with a second currentwaveform between a second electrode and a workpiece by a second powersupply as said first and second electrodes are moved in unison along awelding path, said first and second power supply each comprising an highspeed switching inverter creating its waveform by a number of currentpulses occurring at a frequency of at least 18 kHz with the magnitude ofeach current pulse controlled by a wave shaper and the polarity of saidwaveforms controlled by a signal, wherein said first and second ACwaveforms have a positive portion and a negative portion and a cycleperiod of about 10-20 ms, said method comprising: (a) determining thepull time of a sustained maintenance of same polarity between saidwaveforms; and, (b) adjusting said waveforms to limit said pull time toless than about 5.0 ms.
 30. An electric arc welding method as defined inclaim 29 wherein said AC waveforms are generally sinusoidal.
 31. Anelectric arc welding method as defined in claim 30 wherein one of saidwaveforms is generally a square AC waveform.
 32. An electric arc weldingmethod as defined in claim 29 wherein one of said waveforms is generallya square AC waveform.
 33. An electric arc welding method as defined inclaim 30 wherein both of said waveforms are generally a square ACwaveform.
 34. An electric arc welding method as defined in claim 29wherein both of said waveforms are generally a square AC waveform. 35.An electric arc welding method as defined in claim 30 wherein one ofsaid waveforms is a pulse AC waveform.
 36. An electric arc weldingsystem as defined in claim 19 wherein one of said waveforms is a pulseAC waveform.
 37. An electric arc welding method as defined in claim 29wherein the welding process is submerged arc.
 38. An electric arcwelding method as defined in claim 19 wherein the welding process issubmerged arc.
 39. An electric arc welding system as defined in claim 11wherein said system is a submerged arc system.
 40. An electric arcwelding system as defined in claim 1 wherein said system is a submergedarc system.